The invention relates to a contactor apparatus comprising an electromagnet controlling a multiplicity of power contacts and means for automatically opening these contacts which react when overloads appear in a power circuit on the one hand for separating independently of the electromagnet and by means of a magnetizable part and coil placed in series in this circuit, a mobile power contact (belonging to this circuit) from a fixed contact with which cooperates and for opening, on the other hand, a control switch placed in series with the coil of the electromagnet, this switch being able to be opened by means of a local control member which is adapted to close the contacts again.